Characterizing Salt-Affected Soils

Still another special problem in CEC and ESP determinations occurs for soils of high pH containing significant amounts of the slightly soluble zeolite minerals. Zeolites such as analcime and leucine contain replaceable monovalent cations in their crystal lattices. These structural cations are readily displaced by other monovalent cations, but not by divalent cations. If a monovalent cation is used as the index or 

The traditional classification of salt-affected soils in the United States has been based on the soluble salt (EC) concentrations of extracted soil solutions and on the exchangeable sodium percentage of the assodated soil. The dividing line between saline and nonsaline soils was established at 4 dS m-1 for water extracts from saturated soil pastes. Salt-sensitive plants, however, can be affected in soil whose saturation extracts have ECs of 2 to 4 dS m l. The Terminology Committee of the Soil Science Sodety of America has recommended lowering the boundary between saline and nonsaline soils to 2 dS m-1 in the saturation extract. 

The traditional and recently proposed classification categories for salt-affected soils are given in Table 11.1. Saline (white alkali) soils are those in which plant growth is reduced by excess soluble salts. These soils can be converted to normal soils by leaching the excess salts from the plant root zone. The pH of saline soils 

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Soils are said to be sodic if they contain an excess of sodium. According to their content of salts and sodium, soils are grouped in saline-nonsodic, saline-sodic, nonsaline-sodic, and normal soils. In arid regions, soils rich in sodium are widely distributed due to salt accumulation as sodium chloride and sodium sulfate. The salt-affected soils are chemically characterized by the specific conductivity (mS-cm ) [S = Siemens] of the saturation extract and the saturation of the CEC (%) with sodium. The major cationic constituents of the soluble salts in saline soils are sodium, calcium, and magnesium. Precipitation of Ca and Mg as carbonates effects an increase in the proportion... 

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